Effect of defects in the rare-earth sublattice of the Kondo insulator YbB<Subscript>12</Subscript> on its spectral characteristics and magnetic susceptibility

The results of measuring the static and dynamic magnetic susceptibilities of several series of samples, which are based on the YbB₁₂ Kondo insulator and are substituted in the rare-earth sublattice, are analyzed. Substitution is performed by nonmagnetic isoelectronic Lu ions; magnetic isoelectronic Tm ions; and nonisoelectronic nonmagnetic Y, Sc, and Zr ions. The static susceptibility is measured by a SQUID magnetometer in weak fields, and the dynamic susceptibility is determined from inelastic neutron scattering data. The magnetic properties are simulated using the spectral function found from neutron experimental data. A one-to-one correspondence is established between the influence of an impurity on the initial neutron spectrum and the temperature dependence of the static susceptibility. The results obtained allow one to analyze the relation between the magnetic properties and the electronic structure of the compounds of the given class.     

Passively mode-locked Raman laser

We report on the observation of a mode-locked laser generated with a crystalline whispering gallery mode resonator pumped with a continuous wave laser. Optical pumping of the resonator generates an optical frequency comb with phase locked components at the Raman offset of the resonator host material. Phase locking of the modes is confirmed via measurement of the radio-frequency beat note produced by the comb on a fast photodiode. Neither the conventional Kerr comb nor hyperparametric oscillation is observed when the comb is present. We present a theoretical explanation of the effect.     

Syntheses and crystal structures of new aurate salts of adenine or guanine nucleobases

Two new gold(III) complexes with adenine or guanine nitrogenous bases as counter‐cations were synthesized. These are 6‐amino‐7H‐purine‐1,9‐diium tetrachloridogold(III) chloride monohydrate, (C₅H₇N₅)[AuCl₄]Cl·H₂O, 1 , and 2‐amino‐6‐oxo‐6,7‐dihydro‐1H‐purin‐9‐ium tetrachloridogold(III) hemihydrate, (C₅H₆N₅O)[AuCl₄]·0.5H₂O, 2 . Their crystal structures were studied using single‐crystal X‐ray diffraction and FT–IR spectroscopic techniques. The arrangement of species in the studied crystal structures implies π‐stacking interactions, as well as concomitant C—H…π interactions, hydrogen bonds and other types of noncovalent interactions, which were studied qualitatively and quantitatively using the method of molecular Voronoi–Dirichlet polyhedra. The variation of the nitrogenous base from adenine to guanine results in evident differences in the packing of the species in the crystals of 1 and 2 . The splitting and shifting of bands in the FT–IR spectra of the title compounds reveals several features representative of noncovalent interactions in their crystal structures.     

Oxidation of Aromatic Compounds: XI. Oxidation of Methyl 3-(4-Methoxyphenyl)propynoate in the System CF3COOH-CH2Cl2-PbO2

Oxidation of methyl 3-(4-methoxyphenyl)propynoate in the system CF₃COOH-CH₂Cl₂-PbO₂ at 0-2°C within 2 h affords in a preparative yield of 55% a product of oxidative dimerization, dimethyl 2,3-bis(4-methoxyphenylcarbonyl)but-2-ene-1,4-dicarboxylate (II) whose double bond is in E-configuration according to X-ray diffraction data.     

Microcavity‐Stabilized Quantum Cascade Laser

Narrow‐linewidth lasers are key elements in optical metrology and spectroscopy. Spectral purity of these lasers determines accuracy of the measurements and quality of collected data. Solid state and fiber lasers are stabilized to relatively large and complex external optical cavities or narrow atomic and molecular transitions to improve their spectral purity. While this stabilization technique is rather generic, its complexity increases tremendously moving to longer wavelenghts, to the infrared (IR) range. Inherent increase of losses of optical materials at longer wavelengths hinders realization of compact, room temperature, high finesse IR cavities suitable for laser stabilization. In this paper, we report on demonstration of quantum cascade lasers stabilized to high‐Q crystalline mid‐IR microcavities. The lasers operating at room temperature in the 4.3‐4.6 μm region have a linewidth approaching 10 kHz and are promising for on‐chip mid‐IR and IR spectrometers.

     

Nonlinear optics and crystalline whispering gallery mode cavities

We demonstrate parametric frequency doubling in a whispering gallery cavity made of periodically poled lithium niobate. This demonstration is an example of utility of such crystalline optical whispering gallery resonators with very high Q factors, which we have fabricated.     

Tunable delay line with interacting whispering-gallery-mode resonators

We theoretically study a parallel configuration of two interacting whispering-gallery-mode optical resonators and show a narrowband modal structure as a basis for a widely tunable delay line. For the optimum coupling configuration the system can possess an unusually narrow spectral feature with a much narrower bandwidth than the loaded bandwidth of each individual resonator. The effect has a direct analogy with the phenomenon of electromagnetically induced transparency in quantum systems for which the interference of spontaneous emission results in ultranarrow resonances.     

Whispering gallery resonators for studying orbital angular momentum of a photon

We propose a simple method for generation and detection of photons with nonzero angular momentum. The method utilizes high-quality factor ring resonators that transform a plane electromagnetic wave into a wave with nonzero angular momentum, and vice versa. We show that the method is especially promising for studying high-order Bessel beams, unreachable by other techniques.